The present invention relates to a sewing machine for producing an edge-parallel seam in a workpiece. In particular, the sewing machine is installed with a supporting surface and a presser foot for the workpiece, a stitching needle, a feeding device for advancing the workpiece in a feed direction relatively to the needle, and edge guide means laterally arranged with respect to said needle and with respect to said feed direction. The edge guide means incorporates guide members that are relocatable.
A sewing machine of such type is known by an English specification sheet (Adler-Automation 961-24-1, SpP 2412-E-x-0184-Ti-3). This sewing machine is employed for the sewing or the top-stitching of small parts as shirt cuffs and collars. Such small parts will be provided with edge-parallel seams, wherein the distance between the seam and the edge--also known as stitch width--is mechanically pre-adjustable.
Small parts of the aforementioned type can be profiled with corners. For stitching such corners it is known from the conventional sewing process to bring the needle in its lowest position at the standstill of the machine, lift the presser foot and subsequently tilt the workpiece about the needle until the following edge of the workpiece is again parallelly aligned with respect to the feed direction initiated by the feeding device of the sewing machine. In order to accomplish this tilting about the needle without hindrance of the tip of the workpiece corner by the edge guide, e.g. the stop, it is already known from the German Auslegeschrift No. 1 049 678 to displaceably arrange such stop and to carry out the relocation of this stop by a solenoid, which is controllably connected with the lifting of the presser foot.
In the first-mentioned sewing machine there is employed a control, in which there is integrated the control of the operation description above in order in accomplish the tilting of the workpiece about the needle without difficulty. Moreover, this known sewing machine renders possible the generation of different parallel seams having different seam widths. For this purpose there can be adjusted two different values of width, i.e. distances between the individual seam and the outer edge of the workpiece. At the actual sewing operation this different width can be called off by a program selection of the control.
The foregoing details of the generation of parallel seams or the operation for tilting of a workpiece at its corner is rendered possible, by equipping the sewing machine with two individually controllable edge guide members, which are laterally arranged of the needle and which are relocatable by means of controllable pneumatic cylinders. Moreover, it is possible to relocate the edge guide member situated in a farmost position seen in sewing direction, behind the needle, into three positions as the outer edge guide member is relocatable into two positions. Due to the relocation of the edge guide members in the close vicinity of the supporting area of the workpiece, it is required to displace the edge guide members over a relative large distance in order to render possible the sewing of workpieces having a zone at the starting point or the end point of a seam provided with a projecting section. A typical example of such a workpiece is represented by the so-called one-piece collar of a shirt or a blouse.
One-piece collars differ from the two-piece collar in that the band-formed portion, which later will surround the neck of a person, forms "one-piece" together with another collar part, the so-called upper collar, as the two-piece collar is composed of two pre-manufactured parts.
Due to the projecting areas, as described, it is required to bring one of the edge guide members out of the tilting zone of the workpiece. At collars, the projecting area--also called the beak of the collar--can project up to 2.5 cm with respect to the outer edge of the workpiece, so that it is time-consuming to withdraw or to relocate the edge guide members at sewing machines of the known type having an automatic sequence of operations. Moreover, styles of collars are subject at a high rate to influences of fashion, so that it may occur that the angle formed by the beak of the collar and the outer edge of the collar is less than 90.degree.. Due to this geometric feature, it is not possible to withdraw an edge guide member operating in close contact with the supporting surface, if the edge guide member got caught behind the beak of the collar at the termination of the seam.
Moreover, the top-stitching of one-piece collars is associated with difficulties, as the workpiece of such a special type has a projecting area at the seam start and the seam end. Due to this feature is is required to relocate or withdraw the one or the other edge guide member at the start or the end of the seam to be produced out of the operating zone of the projecting area.